The present invention relates to improved lamp holders for fluorescent cold cathode lamps.
Cold cathode fluorescent lamps are well known to the art and comprise an elongated internally phosphor coated glass tube filled with one or more gases which when excited by an electrical signal form a plasma which causes the coating to fluoresce and to illuminate the environment.
In a cold cathode lamp, the tube, which is generally about one inch in diameter, is typically bent into different shapes and includes at its opposite ends right angle on perpendicular tubular electrode end sections. Each perpendicular section contains an electrode a portion of which comprises an external circular cylindrical metal sleeve over the extremity of the right angle section. The end of the sleeve terminates in a metal end cap. The metal sleeve and metal end cap are in electrical connection with the lamp internal cathode portion in the right angle lamp section and form a contact which is inserted into a mating lamp socket for energizing the lamp. These lamps operate at relatively high power and low temperature.
A lamp holder including a socket for the cold cathode lamps typically includes a ceramic housing having a cavity divided into a terminal section, including a terminal to which a power supply cable is electrically connected, and a socket section containing a U-shaped bronze contact with a resilient portion. The contact resiliently engages the metal sleeve releasably holding the lamp in place by friction and electrically connects it to the lamp electrode via the metal sleeve and end cap. The terminal is connected to the contact. The housing cavity is divided by a phenolic sheet member bonded in place.
The ceramic housing has an apertured wall. An end of an electrical cable is inserted into the cavity through the aperture and connected to the terminal. A ceramic housing cap is fastened over the terminal section after the cable is connected. This lamp holder may be installed by electrical contractors into building structures.
The above-described "slate-of-the art" configuration, however, is subject to potential problems when a contractor hooks up the cable to the terminal during installation in the field.
In the prior art lamp holder, an end of the cable and greenfield assembly are coupled to the lamp holder by loosely passing the greenfield and cable into the housing cavity. The cable wire is then attached to the terminal of the lamp holder by the contractor. The cable and greenfield at their opposite ends, which may be 30-40 feet or more in length, are connected to the remainder of the wiring system.
The present invention provides a solution to the problems and deficiencies of the prior art lamp holders. In accordance with an embodiment of the present invention, a new and improved lamp holder for a cold cathode fluorescent lamp having a pair of spaced electrodes comprises a ceramic housing including a plurality of side walls and a bottom wall defining a cavity therein, one of the walls having an aperture therethrough. An electrical contact is in the cavity for releasably electrically receiving one of the electrodes. A electrically conductive terminal is electrically connected to the contact, the terminal having a terminal portion adapted to receive in conductive contact an electrical wire, the terminal portion being adjacent to the aperture. A ceramic member is secured to the one apertured wall over the aperture, and it has a conduit dimensioned to receive and secure greenfield tubing therein. The ceramic member is dimensioned to mate with the one wall to enclose the aperture at the interface with the one member. The conduit is in communication with the aperture such that a cable contained within and extending from the greenfield tubing can extend into the cavity through the aperture.
In accordance with one preferred embodiment of the invention, the ceramic member is a tube, while in a second preferred embodiment, the ceramic member is secured to the one wall with an adhesive bonding medium.
In a third embodiment the conduit has a length sufficient to provide free air space to preclude electrical shock hazard at the distal end of the conduit when the terminal receives a current of at least about 100 milliamps at 15 kv.
In yet a further embodiment, a length of the greenfield tubing and a length of the cable are each disposed within the conduit and extend from the ceramic member. The cable includes a wire, one end of which is electrically connected to the terminal, the tubing being secured within the conduit to the ceramic member.